Author 5.4 Michael L. Gernhardt Joseph P. Dervay James M. Waligora Extravehicular Daniel T. Fitzpatrick Johnny Conkin Activities

Introduction

The was designed to provide crew and cargo external life support hoses, which could reduce mobility, transit from Earth to low-Earth orbit and back for conducting present snag , and reduce overall reliability. The a wide variety of scientific experiments; deploying and cap- shuttle EMU also was designed to incorporate modular turing of and scientific ; and providing a gloves and boots, and the boots were designed to be means by which to transfer crew and equipment to and from compatible with foot restraints to support working in future space stations. Space shuttle extravehicular activities microgravity. (EVAs) were initially anticipated to be used only for contin- gencies and, thus, were focused on addressing a variety of mal- The suits were designed to operate at the lowest functions associated with the deployment of radiators and reasonable to minimize differences in pressure antennas and the closing and latching of the payload bay doors. across the suit and to permit optimal crew member mobility and dexterity for performing EVA tasks. They also provided protection against sickness (DCS) and Evolution of the Extravehicular under nominal and off-nominal conditions by using Activity Suits lower-pressure secondary system regulators. The U.S. spacesuit system, the shuttle/International (ISS) EMU, has a nominal operating pressure of 30 The shuttle spacesuit system, formally called the extrave- kPa (4.3 psia). The atmosphere in both the shuttle and the hicular mobility unit (EMU), was derived from the advanced ISS resembles that on Earth, at a pressure of 100 kPa (14.5 Apollo suit configuration. In the , most psia) and a composition of 79% nitrogen and 21% oxygen. EVAs took place on the lunar surface, where suit durability, This atmosphere represents a major departure from the low- integrated liquid cooling garments, and low suit operating pressure, high-oxygen- environments aboard (25.8 kilopascals [kPa] or 3.75 pounds per square previous spacecraft. This combination of cabin atmosphere inch absolute [psia]) were required to facilitate relatively and suit pressures required the development of special lengthy EVAs that included ambulation and significant protocols to protect against DCS, which can result when a physical workloads. Metabolic rates during those EVAs crew member shifts rapidly from the relatively high-pressure averaged 1000 BTU/hour, with peaks of up to 2200 cabin to a low- without sufficient time for 8 BTU/hour. The Apollo spacesuit, which had more than 15 denitrogenation (the elimination of nitrogen in lungs and components, included a biomedical belt for capturing and tissues via pure oxygen). DCS can result from gas transmitting biomedical data, urine and fecal containment phase separation and bubble growth in various tissues. systems, a liquid cooling garment, a communications cap, a Depending on the location and degree of gas phase modular portable life support system, a boot system, thermal separation, DCS symptoms can range from minor joint overgloves, and a bubble helmet with eye protection. The discomfort to serious cardiopulmonary or central Apollo left a 34.4-kPa (5-psia) 100% oxygen envi- neurological symptoms that can result in physical disability ronment in the lunar to perform as many as 3 EVAs or loss of life. per mission on the lunar surface. The shuttle EMU incorp- orated many of the same components as the Apollo suit In addition to the risk of DCS, several other environmental system, but, like the shuttle vehicle, the suit was designed to and physiological stresses must be addressed or controlled be reusable. for crew members to safely undertake EVAs. These include, but are not limited to: thermal extremes that range from - The shuttle EMU incorporated a design with 120°C to +120°C, depending on whether the crew member is a range of arm and leg sizing elements that allowed the suits working during the day or at night; the need to provide to be resized for a variety of crew members of different body sources of energy (as much as 200 kcal/hour) to keep up with sizes; the Apollo suits, by comparison, were custom fitted. the metabolic energy expenditure on spacewalks, which can The hard upper torso design also eliminated the need for last 8 hours or longer; the need to provide hydration (as much 1

2 Michael L. Gernhardt, Joseph P. Dervay, James M. Waligora, Daniel T. Fitzpatrick, and Johnny Conkin as 1 liter/hour) and appropriate waste management systems; metabolic rates as high as 1600 BTU/hour, but the previous and the need to provide protection from the radiation, DCS trials had been conducted at work rates of micrometeoroid, and orbital debris environments. The approximately 800 BTU/hour that accurately simulated operating pressure of the suits, as noted above, is 29.6 kPa average EVA work rates. The pilot study had a crossover (4.3 psi), or approximately the same inflation pressure as a design between normal simulated EVA activity and an basketball; this also produces biomechanical constraints in activity profile that included 1 hour of 1600 BTU/hour. Work mobility and dexterity that can result in significant suit- performed during the second hour consisted of nominal induced trauma to the shoulders, wrists, and fingernails as activities. The high-intensity exercise protocol was a zero- well as trauma from point contact loads as the crew member prebreathe protocol with a final suit pressure of 44.8 kPa (6.5 moves within the stiff, pressurized suit. psi); it resulted in the same R value as the space shuttle protocols without engendering the need for the time-intensive oxygen prebreathe. The hypothesis was that high-intensity Preventing the Development of exercise would increase symptoms and bubbles; however, the only remarkable finding of that crossover study was that the last 2 high-intensity exercise runs done on consecutive days resulted in Type II symptoms, causing the tests to be Protecting against DCS has critical operational implications terminated. Subsequent analyses suggest that a zero-pre- because of the time needed for oxygen breathing to facilitate breathe protocol starting at a pressure of 1 atmosphere (atm) nitrogen elimination before an EVA can be safely performed, may make subjects particularly susceptible to Type II DCS and because of the medical and operational consequences of because the nitrogen elimination half-time of the brain and a DCS episode should one occur. spinal cord is 5 to 7 minutes; hence, an oxygen prebreathe would quickly desaturate the neurological tissues and The shuttle decompression protocols were developed based eliminate the autochthonous bubble formation that produces on findings from several hundred decompression trials that central nervous system symptoms of DCS. The zero- had been performed over a 10-year period. Two protocols prebreathe protocols, in contrast, would begin with supersat- were accepted for shuttle flight operations based on an “R” uration in the brain and spinal cord, even with R values value of 1.65. (The R value is the ratio between the nitrogen equivalent to those of protocols that incorporated some tension in a 360-minute half-time tissue compartment and the degree of oxygen prebreathe. spacesuit pressure.) These protocols consisted of either a 4- hour oxygen “prebreathe” performed while wearing a suit pres- Crews and flight planners preferred to use the 70.2 kPa (10.2 surized to 101.2 kPa (14.7 psia), or a staged decompression psia) staged decompression protocol for operational timeline protocol. In the staged decompression protocol, the crew reasons; consequently, all but 4 EVAs from the space shuttle members “prebreathe” oxygen for 1 hour before the cabin is used this protocol. Also, for operational reasons, the time depressurized to 70.2 kPa (10.2 psia) with 26.5% oxygen. spent at 70.2 kPa (10.2 psia) was typically far in excess of the The entire crew remains at 70.2 kPa (10.2 psia) for a mini- tested 12-hour exposure. Figure 5.4-1 shows the distribution mum of 12 hours, and then the EVA crew members complete of the duration at 70.2 kPa (10.2 psia) during the space another 75 minutes of oxygen prebreathe in the suit before shuttle missions that involved EVAs; it is apparent from this performing the EVA. The final in-suit prebreathe times are a figure that the average time spent at this pressure was over 40 function of the time spent at 70.2 kPa (10.2 psia) and can be hours. as short as 40 minutes, if 36 hours or more have been spent at the reduced 70.2-kPa (10.2-psia) cabin pressure. Shirtsleeve, Equilibration of tissue nitrogen tensions at a given ambient ground-based altitude chamber testing of these protocols 414,15 pressure is generally considered to require 36 hours; there- resulted in a DCS incidence rate of 23.7%, with most of fore, longer in-flight times spent at 70.2 kPa (10.2 psia) would the symptoms being minor joint pain. DCS has never been be expected to mitigate the decompression stress. Figure 5.4-2 reported during more than 140 space EVAs in which these illustrates predicted bubble growth for 12- to 36-hour exposures protocols were used, and the DCS rate has been less than at 70.2 kPa (10.2 psia);7 these theoretical calculations suggest 1.5% during more than 300 ground-based chamber that decompression stresses are very low after spending 24 tests, which were conducted while the subjects wore EMU hours at 70.2 kPa (10.2 psia). garments. In addition to the increased exposure time at 70.2 kPa (10.2 Work Rates and Risk of Decompression psia), the suit itself provides some protection against decom- pression because suited crew members have additional oper- Sickness ational oxygen prebreathe time and higher metabolic rates during prebreathe than do the resting test subjects in the Physical activity during EVA is a significant contributor to 4 laboratory trials. During space flight, a series of configuration the risk of DCS. A pilot study was conducted in 1990 to ad- and leak checks is performed after the crew member dons the dress the implications of high work rates during EVA. The suit, followed by an 8- to 12-minute purge cycle before the pre- EMU environmental control system was designed to handle 5. Multisystem Issues and Countermeasures – 3 Extravehicular Activities

Figure 5.4-1 The duration of exposure at 70.2 kPa (10.2 psia) of individual crew members before performing EVA in a 29.6-kPa (4.3-psia) suit. Note: The EVA crew is notated by the STS flight number or International Space Station increment number, followed by the crew member’s designation (eg, EV no.) for those instances in which more than 1 crew member is possible on that particular flight or mission. (EVA = ; EV = extravehicular; STS = Space Transportation System). (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology and Medicine, Vol V, p. 205, © 2004. With permission of the American Institute of Aeronautics and Astronautics.)

breathe clock is started. Then, during depressurization to and limited logistics support of the ISS precluded its cabin vacuum, the suit pressure is set by positive pressure relief pressure from being reduced to 70.2 kPa (10.2 psia). This valves that keep the suit at 34.4 kPa (5 psia) over the ambient was a major constraint because the crew members with the pressure; this results in more oxygen prebreathe time before most current Space Station Remote Manipulator System the tissues become supersaturated. The combined effect of (SSRMS) training to support the EVA construction were these operations is that the suited crew member spends an space shuttle crew members who would need to remain in the additional 20 to 30 minutes of prebreathing at elevated space shuttle if the hatches were closed. Further, because the oxygen concentration levels. The metabolic rates of crew hatches between the 2 vehicles were closed, time-intensive members “resting in the suit” have also been measured at 6.8 logistics transfers between the shuttle and the ISS could not mL•kg-1•min-1; by comparison, the typical resting metabolic be done while EVAs were being performed. The required 4- rate is approximately 3.8 mL/kg-min. Recent research has hour in-suit prebreathe times were not compatible with the shown that even small increases in metabolic rate can de- EVA timelines and the crew scheduling constraints necessary crease the incidence of DCS, presumably through increased nitrogen washout.2,5,9 The combination of all suit-related operational effects reduces decompression stress on crew members relative to shirtsleeve laboratory subjects and offers an explanation as to why the incidence of DCS in suited, ground-based vacuum chamber tests and space flight EVAs is much lower than the initial laboratory trials used to de- velop these decompression protocols.

International Space Station Assembly and the Prebreathe Reduction Program

As space shuttle crews began EVAs in support of assembling Figure 5.4-2 Theoretical bubble growth during a 6-hour EVA the ISS, a series of new challenges arose. The standard shuttle- after spending 12, 16, 20, or 24 hours at an atmosphere of 70.2 based 70.2-kPa (10.2-psia) staged decompression procedure kPa (10.2 psia) with 26.5% oxygen. (EVA = extravehicular activity). (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space became limiting because it required that the hatch between Biology and Medicine, Vol V, p. 205, © 2004. With permission of the space shuttle and the ISS remain closed, as the large volume the American Institute of Aeronautics and Astronautics.)

4 Michael L. Gernhardt, Joseph P. Dervay, James M. Waligora, Daniel T. Fitzpatrick, and Johnny Conkin to assemble and maintain the ISS. To circumvent these con- until the crew member could be re-pressurized in the , straints, a baseline “overnight campout” protocol in which and the possibility that the presence of sub-symptomatic crew members were to stay in the ISS airlock, pressurized to venous gas emboli (VGE) could increase the risk of Type II 70.2 kPa (10.2 psia), was planned for future ISS EVA DCS in crew members with patent foramen ovale. For these operations. However, that protocol also had significant reasons, the incidence of DCS and Grade IV VGE (on the limitations, including high oxygen use and exposure to 70.2 Spencer scale) were set to be below a threshold at which kPa (10.2 psia) during sleeping periods, when crew mem- Type II DCS had never been reported in a large database of bers’ metabolic rates were low, in addition to lack of comfort altitude-decompression studies by NASA, the U.S. Air , and isolation of the crew members in the airlock. It thus and others. became clear that a new prebreathe protocol would be needed to support shuttle crew EVAs during the early ISS assembly The requirement of having a 95% probability that 2 of 3 crew phase. The Prebreathe Reduction Program (PRP) was initiated members would be available for EVA throughout the ISS in 1997. This program had 4 objectives: (1) to prospectively Program, in combination with these additional medical/oper- define acceptable DCS risk levels based on a combination of ational considerations, led to the following accept/reject limits mission success parameters and medical operational consider- for trials of the reduced prebreathe protocols: ations; (2) to develop, test, and validate a 2-hour prebreathe protocol from saturation at 101.2 kPa (14.7 psia) in time to Accept: DCS ≤ 15% and Grade IV VGE ≤ 20%, at support the first EVA from the ISS on assembly flight 7A; 95% confidence interval (3) to develop further time reductions in prebreathe proto- Reject: DCS > 15% or Grade IV VGE > 20%, at cols, if safely possible; and (4) to develop predictive models 70% confidence interval that would allow DCS risk to be estimated across a range of Reject: Any case of Type II DCS operational circumstances, including different saturation pressures, prebreathe times, exercise levels, and breaks in the These criteria were more conservative than any previous prebreathe period. prebreathe ground trial, including the operational space shuttle and Russian Orlan protocols and a 6-hour resting pre- breathe protocol. Risk Estimation

To develop prospective criteria for acceptable DCS risk, the Countermeasures to Reduce Prebreathe Time impact on missions of different DCS symptoms needed to be assessed against well-defined mission success criteria. A well- A decade of research suggested 2 countermeasures that were defined DCS disposition policy was then developed to sup- operationally feasible and had the potential to reduce pre- port the necessary statistical analyses. To summarize, the DCS breathe time: exercise during oxygen prebreathe and (for Earth- disposition policy stated that if a crew member had 1 Type I based subjects) microgravity simulation. (pain only) DCS incident that resolved completely during re- pressurization to cabin pressure, that crew member would be The exercise countermeasure involved exercising during the allowed to perform another EVA within 72 hours. If a crew oxygen prebreathe period according to a protocol developed member had 2 incidents of Type I DCS on the same mission, at the U.S. Air Force School of Aerospace Medicine: 10-minute he or she would not be permitted to perform EVAs until after dual-cycle ergometry exercise at 75% VO2 peak, with 88% of return to Earth and clearance by the NASA Aerospace the workload in the lower body and 12% of the workload in Medical Board. Also, if a crew member had a single incident the upper body. In ground-based tests of 40 subjects, just 10 of Type II DCS (central neurological or cardiopulmonary minutes of exercise during a 1-hour prebreathe cut the DCS), that crew member would not be permitted to perform incidence of DCS by 50% relative to a control group who EVA until cleared by the NASA Aerospace Medical Board. rested during the 1-hour prebreathe; the incidence of DCS This policy was considered conservative and generally was approximately equivalent to that after a 4-hour resting consistent with the policies developed by the U.S. Air Force. prebreathe (Figure 5.4-3).16 This DCS disposition policy was applied to Monte Carlo simulation results of the entire assembly and to the The other countermeasure, microgravity simulation, required maintenance model of the ISS (484 EVAs) to define the the test subjects to refrain from walking for 4 hours before highest DCS risk consistent with a 95% probability that 2 of and during the simulated EVA. Tests performed at the NASA 3 crew members would always be available to perform EVA , tests constituting the Argo series,3,11,12 throughout the life of the ISS. That analysis revealed the and tests at Duke University13 suggested that non-ambulating highest acceptable risk of DCS to be 21%. subjects had lower decompression stress than ambulating subjects. Figure 5.4-4 shows the results of a crossover study These mission-success-based DCS risk estimates were fur- performed at Duke University13 in which a group of subjects ther reduced to account for other medical operational consid- remained semi recumbent for 4 hours before and during simu- erations such as limitations in on-orbit treatment capabilities, lated EVA at 29.6 kPa (4.3 psia) and the control group was a 30- to 45-minute delay from the appearance of symptoms ambulatory. This protocol included a 3.5-hour oxygen pre- 5. Multisystem Issues and Countermeasures – 5 Extravehicular Activities

Figure 5.4-3 Results of 10 minutes of 75% VO2 peak exercise Figure 5.4-4. DCS episodes noted in ambulatory and in a 1-hour prebreathe protocol before performing simulated nonambulatory subjects performing simulated EVAs at EVA at 29.6 kPa (4.3 psia). (EVA = extravehicular activity; O2 = 29.6 kPa (4.3 psia) after a 3.5-hour oxygen prebreathe. (DCS = oxygen; DCS = decompression sickness). (Reprinted from decompression sickness; EVA = extravehicular activity). Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. and Medicine, Vol V, p. 228, © 2004. With permission of the Space Biology and Medicine, Vol V, p. 229, © 2004. With American Institute of Aeronautics and Astronautics.) permission of the American Institute of Aeronautics and Astronautics.)

breathe. Results showed a significantly lower incidence of minutes of “resting prebreathe.” The final depressurization DCS (Fisher’s exact test p = 0.0008) in the legs of the non- from 101.2 kPa (14.7 psia) to the 29.6 kPa (4.3-psia) suit ambulatory subjects. pressure took place over a 30-minute period. The pressure and profiles were identical during all 4 Although this research suggested that prebreathe efficiency protocols tested; only the exercise dose was changed. Results could be improved, the observed rates of DCS in these experi- of these tests are illustrated in Figure 5.4-6. ments were still higher than the prospectively defined “accept” criteria for validation of the ISS prebreathe protocols. Thus, these 2 countermeasures, exercise prebreathe and microgravity simulation, were integrated to develop an operationally viable prebreathe protocol consistent with ISS assembly and maintenance EVA timelines. A multicenter sequential testing program was initiated and led by the NASA Johnson Space Center with decompression testing occurring at Duke University, the University of Texas Hermann Health Science Center, and the Canadian Defense and Civil Institute for Environmental Medicine.6 Figure 5.4-5 PRP Phase I to IV 2-hour oxygen prebreathe exercise protocols. Exercise varied from the 10 minutes of heavy exercise at 75% -1 -1 Four different protocols were tested using various VO2 peak, to 95 minutes of light activity (5.8 mL•kg •min ) that was combinations of high-intensity activities (75% VO2 measured during the normal EVA preparations of configuring and donning peak) and “light activities” (VO of 5.8 mL•kg-1•min-1). the suit. (PRP = Prebreathe Reduction Program; EVA = extravehicular 2 activity). (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. All of the protocols included 2 hours of oxygen pre- Space Biology and Medicine, Vol V, p. 229, © 2004. With permission of the breathe time, but each involved exercise at different American Institute of Aeronautics and Astronautics.) times and different intensities during that period. An overview of the protocols is shown in Figure 5.4-5. The initial test of the U.S. Air Force exercise prebreathe All 4 protocols incorporated a 2-hour oxygen prebreathe as protocol (“Phase I”) during a 2-hour oxygen prebreathe well as a depress to 70.2 kPa (10.2 psia) and 26.5% oxygen resulted in a DCS rate of 19%. Two other protocols that after the initial exercise to avoid the uptake of nitrogen when incorporated only light exercise resulted in DCS rates of 22% donning the spacesuit. After the 30-minute simulated suit- (“Phase III” protocol) and 14% DCS (“Phase IV” protocol). donning period, the pressure was increased to 101.2 kPa Only the Phase II protocol met the accept conditions for (14.7 psia), where the subjects completed an additional 40 operational use (ie, DCS ≤ 15% and Grade IV VGE ≤ 20% at

6 Michael L. Gernhardt, Joseph P. Dervay, James M. Waligora, Daniel T. Fitzpatrick, and Johnny Conkin

Figure 5.4-6 Observed episodes of DCS and Grade IV VGE during testing of each of the 4 Prebreathe Reduction Program protocols (“phases”). Bars indicate the upper bound of the 95% confidence limits. The black dashed line depicts the “accept” level for the number of episodes of DCS (ie, ≤15%); the grey dotted line depicts the “accept” level for the number of episodes of VGE (ie, ≤ 20%). (DCS = decompression sickness; VGE = venous gas emboli). (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology and Medicine, Vol V, p. 229, © 2004. With permission of the American Institute of Aeronautics and Astronautics.)

95% confidence interval). That protocol incorporated a 10- to meet the certification requirements for operating in the minute 75% VO2 peak exercise period coupled with 40 100% oxygen environment of the suit, the decision was made minutes of intermittent light exercise at 5.8 mL•kg-1•min-1, to add a further 20 minutes of oxygen prebreathe time while followed by a 30-minute suit donning period at 70.2 kPa in the suit. These procedures were finalized and used to (10.2 psia), and 26.5% oxygen, followed by a 40-minute perform the first EVA from the ISS, during STS-104, ISS resting prebreathe period at 101.2 kPa (14.7 psia). Tests of assembly Flight 7A (Figure 5.4-7). that protocol resulted in no cases of DCS and 6 cases of Grade IV VGE among 45 subjects. Because these results met The exercise prebreathe protocol had several operational the prospectively defined accept criteria, this protocol was advantages, including more efficient EVA preparation time- accepted for flight operations. Neither heavy nor light lines and the ability to leave the hatches open between the exercise by itself was sufficient to protect against DCS at shuttle and the ISS while the shuttle vehicle was docked to acceptable levels. However, the combination of heavy the ISS. When this chapter was written, the exercise pre- exercise followed by light exercise and then a resting pre- breathe protocol had been used on 42 EVAs from the ISS and breathe met the accept conditions. Recent research also had played an important role in the success of the early suggests that depressurization to 70.2 kPa (10.2 psia) shuttle-based assembly flights. Table 5.4-1 presents data followed by re-pressurization to 101.2 kPa (14.7 psia) and from the early uses of the protocol. The actual prebreathe additional oxygen prebreathe contributes significantly to times for each phase of the protocol are longer than the 5,6,10 reducing decompression stress. required times. In practice, crews never spend less time prebreathing 100% oxygen than is required and often spend Detailed flight procedures were then developed together with more, which, in combination with the additional “operational special exercise and breathing equipment (prebreathe mask, prebreathe time” associated with configuration, communica- hose, and regulators) that would provide the high ventilation tions, leak checks, and oxygen purges, plus the increased rates necessary to support the 10-minute heavy exercise metabolic rates associated with these suited activities (Table period for very fit EVA crew members. An in-flight DCS vali- 5.4-2), adds another degree of conservatism relative to ground- dation program also was developed that included the use of based laboratory trials. an in-suit Doppler bubble detector. When this detector failed 5. Multisystem Issues and Countermeasures – 7 Extravehicular Activities

Figure 5.4-7 The first in-flight use of the exercise prebreathe protocol (left) and the first EVA from the U.S. airlock “Quest” during STS-104, ISS assembly flight 7A (right). (EVA = extravehicular activity; ISS = International Space Station). (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology and Medicine, Vol V, p. 230, © 2004. With permission of the American Institute of Aeronautics and Astronautics.)

Medical Management of Potential

Decompression Sickness Incidents

As part of defining acceptable levels of risk of DCS for the from the U.S. Navy and the U.S. Air Force. The DCS treatment ISS era, the methods by which DCS is treated were revisited literature and DCS databases were extensively reviewed. One by a multidisciplinary team established at the NASA Johnson of the key findings from this effort was the recognition of the Space Center to formulate a DCS . This need for an operational classification system for various team included representatives from Medical Operations, the degrees of DCS symptoms, together with the responses Office, flight controllers, the EVA support team, necessary for efficient re-pressurization of affected crew and Mission Operations Directorate as well as representatives members in the airlock while simultaneously maintaining the

Table 5.4-1 Early uses of the exercise prebreathe protocol, showing actual prebreathe times for each phase of the protocol vs. the nominal required times. Actual time always exceeds the required time for a variety of operational reasons. (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology and Medicine, Vol V, p. 230, © 2004. With permission of the American Institute of Aeronautics and Astronautics.) Nominal time 80 minutes 20 minutes 30 minutes 60 minutes 30 minutes Actuals 80-124 (88) 20-45 (30) 42-104 (61) 60-64 (60.3) 35-70 (39) 70.2-kPa (10.2-psia) Time @ 70.2 kPa Mission Mask Prebreathe In-suit Prebreathe Depressurization Depressurization (10.2 psia) STS-104-1 97 45* 59 60 70********* 110-1 95 30 45 60 40 110-2 80 26 63 60 43 110-3 80 23 46 60 40 110-4 124 74 32 60 41 111-1 82 24 81 60 41 111-2 87 34 70 60 39 111-3 80 25 61 87 33 112-1 102 29 87 60 43 112-2 80 25 62 60 42 112-3 80 24 53 61 38 113-1 94 25 60 60 35 113-2 81 21 49 60 37 113-3 80 25 104 60 42 Exp-4-1 85 20 42 60 59 Exp-6 87 29 63 64 57

8 Michael L. Gernhardt, Joseph P. Dervay, James M. Waligora, Daniel T. Fitzpatrick, and Johnny Conkin

Table 5.4-2 Average and maximum metabolic rates and EVA durations associated with representative ISS assembly tasks. (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology and Medicine, Vol V, p. 231, © 2004. With permission of the American Institute of Aeronautics and Astronautics.) Mission EVA Metabolic Rate (kcal/hour) EVA Duration Maximum Average STS-104 1 788.01 230.4 ± 105.2 5:59 2 492.51 193.4 ± 80.0 6:29 3 492.51 229.0 ± 79.4 4:02 STS-110 1 472.81 224.8 ± 69.7 7:48 2 866.81 198.7 ± 74.2 7:30 3 433.41 198.6 ± 67.5 6:27 4 394.01 199.3 ± 59.9 6:37 STS-111 1 394.01 191.5 ± 61.7 7:14 2 374.31 191.9 ± 66.9 5:00 3 510.42 195.7 ± 67.4 7:17 STS-112 1 610.71 254.9 ± 86.0 7:01 2 476.83 233.8 ± 73.3 6:04 3 394.01 215.7 ± 66.7 6:36 STS-113 1 965.32 228.2 ± 89.1 6:45 2 453.11 213.6 ± 73.2 6:10 3 N/A N/A 7:00 Exp-4 1 413.71 203.2 ± 68.0 5:49

space shuttle in a safe configuration for reentry. The op- (pain-only) symptoms (96%). For this reason, the decision erational DCS classification system was integrated with the was made to initially leave the crew member pressurized in the EVA malfunction , which EVA crew members wear suit at 29.6 kPa (4.3 psi) over cabin pressure while breathing on their forearms. This EVA “cuff classification” system rep- 100% oxygen. Another tenet of treatment involves treating resents an “operational” classification of DCS symptoms. A not just symptoms but also gas bubbles, and for this reason as crew member experiencing symptoms during an EVA many as 2 more hours of breathing oxygen was recom- verbally reports to Mission Control a “cuff class” number mended after symptom resolution. A significant percentage based on symptoms and level of interference with per- of Type II (serious) symptoms also are anticipated to formance. A preestablished response plan is then followed improve with return to . However, that may include termination or abort of an EVA with appro- procedures and hardware were developed to be able to install priate “safing” activities of the shuttle/ISS EVA worksite, as the bends treatment unit while the suit was pressurized and required. By establishing predetermined operational while the crew member was breathing oxygen, which pro- responses, this standard system for communicating symp- vided the capability to increase suit pressure if more serious toms to the Mission Control team is designed to maximize symptoms did not respond to compression to 29.6 kPa (4.3 the health and safety of crew members. The cuff classifica- psi) above cabin pressure. Unless an affected crew member is tion system also serves as the basis for formulating simulated severely compromised, he or she would remain in the suit DCS scenarios for the Mission Control flight team and EVA during the initial phases of treatment, with the spacesuit crew members to rehearse during pre-mission training. serving as the treatment vessel. Many technical aspects must be considered when addressing the challenges of treating a Algorithms or decision trees were then developed for the suited crew member, including communications, EMU and treatment of DCS based on the general concepts of diving vehicle configuration, suit consumables, and airlock re-pres- treatment tables. The principal tenets of treatment include surization procedures. Treatment outlines were subsequently oxygen and pressure over time, with fluids and medications converted into malfunction procedures that follow the used as adjuncts. In the previous version of space DCS checklist format and decision trees that astronauts are treatment, crew members were returned to cabin pressure as accustomed to using. soon as possible, after which the suit was depressurized to cabin pressure. After this the crew member breathed cabin air As described in detail elsewhere in this book, medical kits for approximately 30 minutes. A “bends treatment apparatus” were flown on the space shuttle and are being flown on the was installed on the suit providing the capability to increase ISS. Although these kits are necessarily constrained in terms the suit pressure to up to 57.2 kPa (8.3 psi) above cabin of size and , they are designed to address a broad pressure. Database analysis suggested that the return to cabin range of medical conditions based on prior space flight pressure from the 29.6 kPa (4.3-psia) hypobaric environment experience and anticipated illnesses and injuries. Medical of the spacesuit would be sufficient to treat most Type I treatment procedures after the suit is doffed (removed) 5. Multisystem Issues and Countermeasures – 9 Extravehicular Activities includes the administration of oral or intravenous hydration to support the high frequency of EVAs anticipated in future and additional oxygen by facemask. The shuttle medical kits Exploration Class missions, which includes a requirement for contained 3.1 L of normal saline (0.9% NaCl); and 12.1 L of a work efficiency index greater than 3.0. normal saline are available aboard the ISS. At present, no other adjunct medications are currently flown for the specific support of DCS treatment. Approach to Extravehicular Activity Medical Monitoring A simple DCS neurological examination that can be per- formed on an EVA crew member by a nonphysician astro- naut was developed as a tool to assess signs and symptoms Before flight, Flight Surgeons coordinate with members of over time. This examination assesses chiefly motor and the Astronaut Conditioning, Strength, and Rehabilitation neurological functions, and can be used to evaluate crew team to ensure that all EVA crew members have a well- members who are either fully suited or with the suit doffed. balanced exercise regimen. Emphasis is placed on upper- extremity strength and endurance because EVAs require “Flight rules” are preestablished procedures developed for intensive use of hands and arms. the Flight Control Team in Mission Control to respond to a variety of potential mechanical and operational scenarios During flight, all EVAs are preceded and followed by throughout all phases of flight. The purpose of flight rules is assessments of medical fitness. The primary focus of a pre- to avoid miscommunications across disciplines and to maxi- EVA medical evaluation is to identify any medical issues that mize effective decisions. Flight rules developed for EVA would constrain or potentially harm crew members during deal with “oxygen payback” ratios for air breaks in pre- EVA. Post-EVA medical evaluations aim to ensure continued breathe periods; they also specify deorbit requirements to crew member health and identify potential suit-related health designated worldwide Primary Hyperbaric Care sites, and issues. On the day before an EVA was to take place, the address resolved and unresolved “cuff class” symptoms. Flight Surgeon held private medical conferences with each Expertise both within and outside NASA has been leveraged shuttle EVA crew member to assess his or her rest, hydration, to create and implement a system that is now in place to more and nutrition status as well as any physical issues that might effectively address potential cases of DCS on orbit. have affected his or her EVA performance. For ISS missions, medical clearance and certification are based on medical assessment, which includes a review of recent counter- Extravehicular Activity Frequency measures performed to ensure adequate aerobic capacity and strength. This medical evaluation, which is completed 24 and the Work Efficiency Index hours before a scheduled EVA, consists of a review of physiological systems by the Flight Surgeon, a brief skin and The actual EVA is part of a long workday that includes pre- extremity examination by the on-board Crew Medical EVA preparation, suit donning, prebreathe, airlock decom- Officer, and a urinalysis to ensure proper hydration status. pression, conducting an EVA that can last more than 8 hours, On the day of the EVA, the crew member’s vital signs (blood reentering and securing the airlock, re-compressing the pressure, body ) are measured and the Flight airlock, and doffing the spacesuit. Thus, back-to-back days of Surgeon may direct further medical examination based on EVA would be overly fatiguing. To quantify the time results from the previous review of systems. required for each of these functions, an EVA work efficiency index was created and is defined as EVA time/total time for The Surgeon Console position in Mission Control is staffed EMU and airlock preparation + prebreathe time + airlock by both a Flight Surgeon and a biomedical engineer during depressurization + airlock re-pressurization + total after-EVA EVAs to provide medical support as needed. Additional EVA activities. Table 5.4-3 shows work efficiency indices for medical and physiological experts are available on call to shuttle and ISS EVA operations. Clearly significant amounts assist the console surgeon should further consultation be of time are required to prepare all of the individual elements required. Biomedical monitoring is undertaken to provide of the suit and airlock: from configuring the biomedical feedback to the Flight Director. Monitoring includes monitoring system to filling and installing the in-suit drink electrocardiography and heart rate, suit pressure, suit carbon bag to configuring and checking out the suits and . dioxide , and estimated metabolic rate. During The work efficiency index ranges from approximately 0.39 to EVAs, the crew members have access to an in-suit drink bag 0.51, meaning that more than twice as much time goes into that contains 0.95 L (32 oz) of water, and they wear a preparing for an EVA than is spent actually performing the maximum-absorbency garment for urine absorption as EVA. Significant improvements in this index will be required needed.

10 Michael L. Gernhardt, Joseph P. Dervay, James M. Waligora, Daniel T. Fitzpatrick, and Johnny Conkin

Table 5.4-3 Work Efficiency Index (EVA time [based on a 6.5-hour EVA] per the overhead associated with pre- and post-EVA preparations of the suit and airlock systems). (Reprinted from Katuntsev VP, Osipov YuYu, Gernhardt ML. Space Biology and Medicine, Vol V, p. 208, © 2004. With permission of the American Institute of Aeronautics and Astronautics.) Shuttle Staged ISS CEVIS Exercise Prebreathe Protocol Decompression (12 hours ISS: 4 hours in Suit (Using ISS O2) @ 70.2 kPa [10.2 psia]) EVA Overhead Activities Time in Minutes Time in Minutes Time in Minutes Suit checkout 115 185 185 REBA-powered hardware 25 25 25 checkout SAFER checkout 30 30 30 Airlock configuration 95 90 90 Consumables preparation 60 120 120 EVA preparation – prebreathe 60 0 80 related EVA preparation – EMU related 30 30 30 Suit donning and leak check 60 60 60 Completed during Completed during Completed during SAFER donning prebreathe prebreathe prebreathe Purge 8 12 12 Prebreathe 75 240 60 Airlock depressurization 15 30 40 Airlock egress 15 15 15 Airlock ingress 15 15 15 Airlock re-pressurization 15 15 15 Suit doffing 25 25 25 SAFER doffing and stow 10 10 10 Post-EVA processing 105 90 90 Total 758 992 902

EVA Work Efficiency Index 0.51 0.39 0.43 *Abbreviations: CEVIS = Cycle Ergometer with Vibration Isolation System; REBA = rechargeable EVA battery assembly; SAFER = simplified aid for EVA rescue.

Typically the maximum duration of EVAs as currently neutral pool or in a microgravity environment. planned is 6.5 hours. However, EVAs can and have been Another factor contributing to problems with suit fit is the extended to meet mission objectives if suit consumables are significant increase over time in spinal column dimensions in available and if the Flight Surgeon concurs that the crew mem- a microgravity environment. Moreover, the hard upper torso bers’ physiological parameters are within acceptable limits. design partially restricts scapulothoracic motion, which can result in shoulder rotator cuff impingement during some arm maneuvers. Extravehicular-activity-induced Injuries The padding and harnesses used, the suit humidity (particularly that over the hands and feet), fitting and sizing, anthropometric factors and the crew member’s physical The extensive ISS construction tasks performed during EVAs conditioning, the ranges of motion and force required for have been associated with crew member injuries, both during various tasks, the repetition of those tasks, and recovery Laboratory training and during actual times between EVAs all influence the likelihood and space flight EVAs. In addition to the EVA tasks themselves, prevalence of EVA injuries. Training with heavy tools, the spacesuit design and sizing, foot restraints, suit humidity prolonged inversion, and overhead arm operations all can control, EVA duration, and repetition factors all influence the increase the probability of injury during training in the likelihood of crew member injury. Neutral Buoyancy Laboratory at the NASA Johnson Space Center, and tasks are typically performed multiple times As noted at the beginning of this section, the U.S. spacesuit during training in preparation for one such event during an has a hard upper torso design, and sizing is determined using actual EVA. Although the combination of the crew member, a computer algorithm developed from previous use of such his or her tools, and the EMU during simulations may suits. Because the fitting process takes place at 1g, an injury- collectively be neutrally buoyant, the crew member is not free fit is not necessarily ensured when the suit is used in a weightless within the suit, and hard-point contact and range- 5. Multisystem Issues and Countermeasures – 11 Extravehicular Activities of-motion limitations can and do result, particularly when the References crew member is working in the inverted position.

In a small survey of 22 EVA astronauts at the NASA 1. Conkin J. Preventing Decompression Sickness Over Three Johnson Space Center, 14 reported an EVA-related shoulder Decades of Extravehicular Activity. Houston, Tex: Lyndon B. injury and 10 had experienced a previous shoulder injury. Of Johnson Space Center; 2011. NASA/TP-2011-216147. those who had experienced pain or injury, 56% experienced 2. Conkin J, Gernhardt ML, Powell MR, Pollock N. A Probability shoulder pain or injury during EVA mission training and Model of Decompression Sickness at 4.3 psia After Exercise 18% did so during actual EVA. All 14 subjects experienced Prebreathe. Houston, Tex: Lyndon B. Johnson Space Center; right shoulder pain, and 68% were affected in both shoulders. 2004. NASA TP-2004-213158. Two of the 14 astronauts required surgical repair after injury. Most of the incidents associated with EVA training were 3. Conkin J, Powell MR. Lower body adynamia as a factor to classified as minor and resolved within 48 to 72 hours. reduce the risk of hypobaric decompression sickness. Aviat Space Environ Med. 2001;72:202-214. Injuries of the hands and feet associated with EVAs and EVA 4. Conkin J, Waligora JM, Horrigan DJ Jr, Hadley AT III. The training also have been reported. One NASA study of 770 Effect of Exercise on Venous Gas Emboli and Decompression suited training test events involved 352 reported symptoms. Sickness in Human Subjects at 4.3 psia. Houston, Tex: Lyndon Of these symptoms, 47% involved hands, 21% involved B. Johnson Space Center; 1987. NASA TM-58278. shoulders, 11% involved feet, 6% involved arms, 6% in- volved legs, 6% involved the neck, and 3% involved the 5. Gernhardt ML, Conkin J, Vann RD, Pollock NW, Feiveson trunk. Hand symptoms were primarily fingernail delamina- AH. DCS risks in ground-based hypobaric trials vs. extravehic- tion (loss), thought to be secondary to excess moisture in the ular activity. Undersea Hyperb Med. 2004;31(3):338. EVA gloves, and axial loading of the fingertips. Also present were abrasions, contusions, and 2 cases of peripheral nerve 6. Gernhardt ML, Conkin J, Vann RD , Powell MR. Design of a 2-hour prebreathe protocol for space walks from the impingements related to glove fit and hard-point contact International Space Station (abstract 43). Paper presented at: compressions. Crew members in microgravity and on the 71st Annual Scientific Meeting of the Aerospace Medical lunar surface have often noted significant hand fatigue re- Society. May 14-18, 2000; Houston, Tex. lated to glove resistance during grasping motions. 7. Gernhardt ML. Development and Evaluation of a Decom- Pain and injury to the feet, chiefly of the dorsal surface of the pression Stress Index Based on Tissue Bubble Dynamics foot and distal toes, were commonly associated with boot-fit [dissertation]. Philadelphia, Pa: University of Pennsylvania; problems, compression in foot restraints, or pressure from 1991. folds in the foot bladder. Elbows were the most common site 8. Horrigan DJ, Waligora JW, Bredt JH. Extravehicular activities. of pain or injury in the arms, as were knees in the legs. In: Nicogossian AE, Huntoon CL, Pool SL, eds. Space Neutral-buoyancy EVA training is often intense as a mission Physiology and Medicine. 2nd ed.. Philadelphia, Pa: Lea and launch date approaches; fingernail delamination and shoulder Febiger; 1989:121-135. injuries may be related to the frequent and large numbers of training sessions. Mitigations targeting the causal factors are 9. Morgenthaler GW, Fester DA, Coolfy CG. An assessment of being progressively implemented and incorporated into the habitat pressure, oxygen fraction, and EVA suit design for designs of the next-generation spacesuits. space operations. Acta Astronautica. 1994;32(1):39-49.

10. Pollock NW, Natoli MJ, Vann RD, Conkin J, Gernhardt ML. Comparison of V-4 and V-5 exercise/oxygen prebreathe Conclusions protocols to support extravehicular activity in microgravity (abstract). Paper presented at: Annual Scientific Meeting of the As of March 2011, 186 EVAs had been conducted by crew Undersea and Hyperbaric Medical Society. June 14-16, 2007; members wearing U.S. spacesuits. All EVAs were successful, Maui, Hawaii. Available at: http:www.uhms.org. Accessed and all crew members returned safely and in good health.1 The September 23, 2011. successful assembly of the ISS, using EVAs originating from 11. Powell MR, Waligora JM, Norfleet WT, Kumar KV. Project the space shuttle, has been one of the most significant ARGO – Gas Phase Formation in Simulated Microgravity. accomplishments in the history of NASA. This success is due Houston, Tex: NASA Lyndon B. Johnson Space Center; 1993. in large part to the care and dedication of the physiological NASA TM-104762. research and medical personnel overseeing virtually every aspect of EVA: from the development of procedures and 12. Powell MR, Horrigan DJ Jr, Waligora JM, Norfleet WT. countermeasures to personnel selection and training and Extravehicular activities. In: Nicogossian AE, Huntoon CL, Pool finally through providing real-time and post-flight medical SL, eds. Space Physiology and Medicine. 3rd ed. Philadelphia, support of EVA crews. Pa: Lea & Febiger; 1994:128-140.

12 Michael L. Gernhardt, Joseph P. Dervay, James M. Waligora, Daniel T. Fitzpatrick, and Johnny Conkin

13. Vann RD, Gerth WA. Is the risk of DCS in microgravity less 15. Waligora JM, Pepper LJ. Physiological experience during than on earth? (abstract 45). Paper presented at: 68th Annual shuttle EVA. Paper presented at: 25th International Conference Scientific Meeting of the Aerospace Medical Association. May on Environmental Systems. July 10-13, 1995; San Diego, 11-15, 1997; Chicago Ill, Calif. SAE Technical Series. No. 951592.

14. Waligora JM, Horrigan DJ, Conkin J, Hadley AT. Verification 16. Webb JT, Fisher MD, Heaps CL, Pilmanis AA. Prebreathe of an Altitude Decompression Sickness Protocol for Shuttle enhancement with dual-cycle ergometry may increase decom- Operations Utilizing a 10.2 psia Pressure Stage. Houston, Tex: pression sickness protection. Aviat Space Environ Med. NASA Lyndon B. Johnson Space Center; 1984. NASA TM- 1996;67:618-624. 58259.